A large heating, ventilation and air conditioning system (HVACS) for a building or other structure may use a chiller to cool or heat water that is used to cool or heat rooms of the building. The chilled or heated water may be caused to flow through coils in a room of the building. Air in the room may be caused to flow through the coils. The coils serve as heat exchangers to enable cooling or heating of the air. Chillers and rooms may have separate control systems. Thus, a thermostat in a room may control or trigger the flow of air through the coils, but not affect operation of the chiller. A separate thermostat or management system may control a set point that determines the temperature to which the water is cooled or heated.
Energy usage of an HVACS may vary according to the square of the difference between the ambient outdoor temperature and the set point temperature of the chiller.